Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The alkylating activity of reduced diaziquone was studied by the nitrobenzylpyridine (NBP) assay and was compared to those of the parent compound and aziridine-containing N,N',N"-triethylenethiophosphoramide (Thio-TEPA). Diaziquone (AZQ) was reduced enzymatically by 2e- using S9 cell fraction from MCF-7 cells which is rich in NAA(P)H:quinone-acceptor oxidoreductase (DT-diaphorase) (QAO) activity. One electron enzymatic reduction was performed with NADPH-cytochrome c reductase. The alkylating activity of AZQ increased 3-fold when reduced by 2e-. This increase was inhibited by dicumarol, an inhibitor of QAO. In contrast, the alkylating activity of AZQ did not increase beyond that of the parent compound when reduced by 1e- using purified NADPH-cytochrome c reductase. Similar results were obtained when AZQ was reduced chemically with borohydride (2e-) and with NADPH (1e-). Anaerobic incubations of AZQ with the S9 fraction of MCF-7 cells (2e- reduction) resulted in an increase in NBP alkylation over its aerobic counterpart (1.8-fold) while maintaining the near 3-fold increase in alkylation over untreated AZQ. In contrast, AZQ incubations with NADPH-cytochrome c reductase (1e- reduction) under the same conditions did not result in an NBP alkylation increase over untreated AZQ. These results indicate that AZQ hydroquinone is most likely the responsible species for the observed alkylation of this antitumor agent to DNA and other nucleophiles. The results also suggest that NAD(P)H:quinone-acceptor oxidoreductase is a very important enzyme in the bioactivation of AZQ.
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PMID:Reductive metabolism of diaziquone (AZQ) in the S9 fraction of MCF-7 cells. II. Enhancement of the alkylating activity of AZQ by NAD(P)H: quinone-acceptor oxidoreductase (DT-diaphorase). 130 Oct 71

Nitroaniline mustards have potential as hypoxia-selective cytotoxic agents, with reductive metabolism activating the nitrogen mustard by converting the electron-withdrawing nitro group to an electron-donating hydroxylamine or amine. However, the parent compounds have poor aqueous solubility, and their potencies are limited by low reduction potentials (E1/2 ca. -600 mV versus the normal hydrogen electrode) and corresponding slow rates of nitro reduction. To address these limitations, a series of 4-nitroaniline mustards bearing hydrophilic side chains attached via an electron-withdrawing carboxamide group was prepared and evaluated for hypoxia-selective cytotoxicity against Chinese hamster cell lines. The N-[(N,N-dimethylamino)ethyl]carboxamide derivatives proved to have excellent aqueous solubility and improved cytotoxic potency, but their reduction potentials, while higher than the non-carboxamide compounds, were still low and little selectivity for hypoxic cells were observed. A series of carboxamides of 2,4-dinitroaniline mustard was also prepared. These compounds had reduction potentials in the desired range (E1/2 ca. -450 mV by cyclic voltammetry) and were more toxic to hypoxic than aerobic UV4 cells. The most selective compounds were 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide (20, SN 23862) and its water-soluble N-[(N,N-dimethylamino)ethyl]carboxamide analogue. These showed selectivities of 60- to 70-fold for hypoxic UV4 cells. The selectivity of 20 was much superior to that of its aziridine analogue (23, CB 1954), which was only 3.6-fold more toxic to hypoxic than oxic cells in the same system. Compound 20 is a much less efficient substrate than CB 1954 for the major aerobic nitroreductase from rat Walker tumor cells, NAD(P)H:quinone oxidoreductase (DT diaphorase). Lack of aerobic bioactivation of 20 by DT diaphorases may be responsible for its higher hypoxic selectivity than that of 23.
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PMID:Hypoxia-selective antitumor agents. 5. Synthesis of water-soluble nitroaniline mustards with selective cytotoxicity for hypoxic mammalian cells. 150 7

The flavoenzyme DT-diaphorase has the potential either to bioactivate or to detoxify different bioreductive cytotoxins. Elucidation of structural features governing the ability to act as a substrate for DT-diaphorase should facilitate rational optimization or elimination of this reductive pathway for a particular class of bioreductive drug. We have examined structure-activity relationships governing both the cytotoxicity and the DT-diaphorase mediated reduction of two groups of bioreductive alkylating agents: (1) Indoloquinones related to EO9 [3-hydroxy-methyl-5-aziridinyl-1-methyl-2-(1H-indole-4,7-dione)prop-beta - en-alpha-ol]; and (2) derivatives of diaziridinyl benzoquinone or diaziquone [2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone]. The rat U.K. 256 Walker tumor cell line and the human HT29 colon carcinoma line were studied because of their high DT-diaphorase content. Enzyme activity was measured spectrophotometrically by dicoumarol inhibitable cytochrome c reduction in the presence of drug, and aerobic cytotoxicity was assessed by the MTT assay. EO9 acted as a good substrate for both enzyme preparations and was highly potent in each cell line, especially in Walker tumor cells (ID50 0.039 nM). AZQ was also reduced efficiently and gave an ID50 of 6 nM in the Walker tumor line. Slight modifications in structure resulted in large variations in both DT-diaphorase metabolism and toxicity for both types of agent. There was a clear tendency for the most efficiently reduced analogues to exhibit greater cytotoxic potency. Inclusion of an aziridine moiety in the structure appears to be desirable, but not essential, for both rapid reduction and cytotoxicity. There was no evidence of active site-directed enzyme inhibition.
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PMID:Structure-activity relationships for DT-diaphorase reduction of hypoxic cell directed agents: indoloquinones and diaziridinyl benzoquinones. 154 32

A series of analogues of the novel hypoxia-selective cytotoxin 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide (6) have been prepared and evaluated, in a search for compounds which retain high hypoxic selectivity but have increased potency and/or aqueous solubility. Several analogues with ionizable or dipolar carboxamide side chains showed improved solubility but generally had reduced cytotoxic potency and hypoxic selectivity. Modification of the mustard leaving groups or replacement of the carboxamide moiety provided some compounds with superior potency, but only the mixed chloro/mesylate mustard 20 provided a gain in potency relative to solubility while retaining the hypoxic selectivity of 6. These nitrogen mustards did not show the remarkable activity demonstrated by the related aziridine 7 [CB 1954, 5-(N-aziridinyl)- 2,4-dinitrobenzamide] in Walker 256 adenocarcinoma cells and are not efficient substrates for the DT-diaphorase which activates the latter compound by aerobic nitroreduction in Walker cells. Variations in hypoxic selectivity within the dinitrobenzamide mustards appear not to be due to differences in sensitivity to activation by this enzyme. Walker cells showed intermediate sensitivity to the mono(2-chloroethyl) analogue 26 but not to the related half-mustard 27, suggesting that the inhibition of DT-diaphorase activity is due to steric effects in the 5-position. The preferred compound overall with respect to solubility, potency, and in vitro hypoxic cell selectivity was the (dimethylamino)-ethyl derivative 11. DNA elution studies and comparison of the sensitivity of AA8 and UV4 cells to this compound indicated reductive activation to form a DNA cross-linking agent under hypoxia. Radiobiological studies indicated 11 to be equally active against both aerobic and hypoxic cells in KHT tumors. It is not clear whether this reflects efficient killing of aerobic cells as a result of diffusion of reduced metabolites from hypoxic regions or whether cytotoxicity in tumors is independent of hypoxia.
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PMID:Hypoxia-selective antitumor agents. 9. Structure-activity relationships for hypoxia-selective cytotoxicity among analogues of 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide. 803 24

NAD(P)H:Quinone Oxidoreductase1 (NQO1) also known as DT-diaphorase is a flavoprotein that catalyzes the two-electron reduction of quinones, quinone imines and azo-dyes and thereby protects cells against mutagenicity and carcinogenicity resulting from free radicals and toxic oxygen metabolites generated by the one-electron reductions catalyzed by cytochromes P450 and other enzymes. High levels of NQO1 gene expression have been observed in liver, lung, colon and breast tumors as compared to normal tissues of the same origin. The transcription of the NQO1 gene is activated in response to exposure to bifunctional (e.g. beta-naphthoflavone (beta-NF), 2, 3, 7, 8 tetrachorodibenzo-p-dioxin (TCDD)) and monofunctional (phenolic antioxidants/chemoprotectors e.g. 2(3)-tert-butyl-4-hydroxy-anisole (BHA)) inducers. The high level of expression of the NQO1 gene and its induction by beta-NF and BHA require the presence of an AP1 binding site contained within the human Antioxidant Response Element (hARE) and are mediated by products of proto-oncogenes, Jun and Fos. Induction of NQO1 gene expression involves transfer of a redox signal from xenobiotics to unknown 'redox protein(s)' which in turn, modify the Jun and Fos proteins for greater affinity towards the AP1 site of the NQO1 gene and activates transcription. The expression and regulation of the NQO1 gene is complex as many additional cis-elements have been identified in the promoter region and is a subject of great future interest. In addition to established tumors, NQO1 gene expression is also increased in developing tumors, indicating a role in cellular defense during tumorigenesis. It has been proposed that low molecular weight substance(s) can diffuse from tumor cells into surrounding normal cells and activate the expression of the NQO1 gene. Purification and characterization of such substance(s) may provide important information in regard to the mechanism of activation of NQO1 gene expression and the role of increased NQO1 expression in tumor development. In view of the general consensus that NQO1 is over-expressed in tumor cells and the realization that NQO1 may either activate or detoxify xenobiotics, it is important to establish the role of NQO1 in the activation, and the detoxification of xenobiotics and drugs and in the intrinsic sensitivity of tumors to bioreductive alkylating aziridinyl benzoquinones such as diaziquone (AZQ), mitomycin C (MMC), and indoloquinone EO9, as well as to the dinitrophenyl aziridine, CB1954, and the benzotriazine-di-N-oxide, SR 4233.
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PMID:NAD(P)H:quinone oxidoreductase1 (DT-diaphorase) expression in normal and tumor tissues. 837 15

The biologic functions attributed to the nucleophosphoprotein p53 have been increasing in recent years. Some studies suggested that wild type p53 is responsible for cell cycle arrest brought about as a response to exposure of mammalian cells to DNA-damaging agents. This cell cycle arrest occurs in order for cells to repair the damaged macromolecules. Extensively damaged cells are also thought to undergo apoptosis via the p53-dependent or -independent signal transduction pathways. In this study, we investigated the ability of diaziridinylbenzoquinones to increase p53 levels in the human breast cancer cell line MCF-7. Diaziquone (AZQ), an anticancer agent, and its derivatives, diaziridinequinone (DZQ) and methyldiaziridinequinone (MeDZQ), induced p53 in a dose- and time-dependent manner as measured by the electrophoretic mobility shift assay. Wild type p53 induction by AZQ was suppressed when DT-diaphorase activity was inhibited by pretreating the cells with dicumarol. Aside from their potent alkylating activity, these agents also undergo redox cycling as evidenced by oxygen consumption and the production of reactive oxygen species (ROS). Inhibition of ROS production by the antioxidant enzyme catalase reduced AZQ- and DZQ-mediated p53 induction by about 45%. Thiotepa, a non-quinone aziridine-containing agent, and 1,4-benzoquinone (p-BQ), a redox cycling quinone, increased p53 levels. The nonalkylator oxygen-radical-generating agent menadione (MD) caused p53 induction only when MCF-7 cells were allowed to recover in drug-free media. On the basis of these data, we propose that the bioreductive activation of AZQ is a prerequisite for p53 induction. Moreover, the induction of p53 by AZQ requires both the quinone and the aziridine moieties of the AZQ molecule. Although AZQ and its analogues increased p53 levels in MCF-7 cells, p53 induction in these cells may not be responsible for the apoptosis seen upon treatment of MCF-7 cells with these agents. The uncoupling of p53 induction and apoptosis is evidenced by the generation of nucleosomal DNA laddering in aziridinequinone-treated T47D cells, a breast cancer cell line bearing a p53 mutation.
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PMID:Induction of p53 by the concerted actions of aziridine and quinone moieties of diaziquone. 954 7

RH1, 3-methyl-6-hydroxymethyl-2,5-diaziridinyl-1,4-benzoquinone, is a NQO1 (NAD(P)H quinone oxidoreductase) directed anti-tumor agent. It is designed as a water soluble analog of MeDZQ (3,6-dimethyl-2,5-diaziridinyl-1,4-benzoquinone) and is a drug candidate for clinical evaluation. A HPLC assay has been developed for its analysis. The assay is sensitive (ldl<0.2 ng), precise (rsd<1%), linear (r(2)=0.9997), accurate (error<0.6%), and stability-indicating. Using the developed assay, aqueous stability of RH1 has been evaluated. Both aziridine rings in MeDZQ are known to be easily hydrolyzable in aqueous solutions, however, hydrolysis of the second aziridine ring in RH1 appears inhibited.
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PMID:Stability-indicating HPLC assay and solution stability of a new diaziridinyl benzoquinone. 1124 89

The synthesis and biological evaluation of a homologous series of conjugates (9-13) of 2,5-diaziridinylbenzoquinone (DZQ) and 9-carbonylacridine, a DNA intercalating moiety, via a polymethylene unit (n=2-6) are described. In addition, the non-acridine compound 14, analogous to compound 12, and the 5-methyl-DZQ derivatized conjugate 15, an analog of compound 10, were also prepared. Through a Comet assay, compounds 9-13 were shown to produce DNA interstrand cross-links at submicromolar concentrations, consistent with K562 leukemia cells accumulating in the G2/M stage in the cell cycle. The cytotoxicity of compounds 9-15 was examined using a MTT assay on several human cancer cell lines, including chronic myeloid leukemia K562, the non-small cell lung cancers H596 and H460, and colon carcinoma cells BE and HT29. H460 and HT29 are rich in DT-diaphorase (DTD), and H596 and BE cells have negligible amounts of functional DTD. Under continuous exposure of drugs, except to the non-aziridine compound 19b, the IC50 values of all other compounds were determined to be in the range of 0.3-11.3 nM. Compound 10, which has a propyl linker group, was subjected to in vivo studies. When BDF1 mice with established mouse mammary carcinoma were treated with compound 10 (2 mg/kg at day 1 and 5 mg/kg at day 7), a significant delay (9-10 days) in cancer growth was recorded when compared to untreated controls. Furthermore, administration of compound 10 to nu/nu BDF1 mice bearing human lung cancer H460 xenograft (1.5 mg/kg for 10 for five consecutive days from day 13 and 17) also showed a significant reduction in tumor growth compared to untreated controls. The half-life of compound 10 in the presence of five different peptidases (porcine esterase, carboxypeptidase A, B and Y, and pepsin) was determined to be between 30 and 60 h.
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PMID:Synthesis and biological evaluation of novel diaziridinylquinone-acridine conjugates. 1450 82

The 5-aziridinyl-2,4-dinitrobenzamide CB 1954 is a substrate for the oxygen-insensitive nitroreductase (NTR) from E. coli and is in clinical trial in combination with NTR-armed adenoviral vectors in a GDEPT protocol; CB 1954 is also of interest for selective deletion of NTR-marked cells in normal tissues. Since little further drug development has been carried out around this lead, we report here the synthesis of more soluble variants and regioisomers and structure-activity relationship (SAR) studies. The compounds were primarily prepared from the corresponding chloro(di)nitroacids through amide side chain elaboration and subsequent aziridine formation. One-electron reduction potentials [E(1)], determined by pulse radiolysis, were around -400 mV, varying little for aziridinyldinitrobenzamide regioisomers. Cytotoxicity in a panel of NTR-transfected cell lines showed that in the CB 1954 series there was considerable tolerance of substituted CONHR side chains. The isomeric 2-aziridinyl-3,5-dinitrobenzamide was also selective toward NTR+ve lines but was approximately 10-fold less potent than CB 1954. Other regioisomers were too insoluble to evaluate. While CB 1954 gave both 2- and 4-hydroxylamine metabolites in NTR+ve cells, related analogues with substituted carboxamides gave only a single hydroxylamine metabolite possibly because the steric bulk in the side chain constrains binding within the active site. CB 1954 is also a substrate for the two-electron reductase DT-diaphorase, but all of the other aziridines (regioisomers and close analogues) were poorer substrates with resulting improved specificity for NTR. Bystander effects were determined in multicellular layer cocultures and showed that the more hydrophilic side chains resulted in a modest reduction in bystander killing efficiency. A limited number of analogues were tested for in vivo activity, using a single ip dose to CD-1 nude mice bearing WiDr-NTR(neo) tumors. The most active of the CB 1954 analogues was a diol derivative, which showed a substantial median tumor growth delay (59 days compared with >85 days for CB 1954) in WiDr xenografts comprising 50% NTR+ve cells. The diol is much more soluble and can be formulated in saline for administration. The results suggest there may be advantages with carefully selected analogues of CB 1954; the weaker bystander effect of its diol derivative may be an advantage in the selective cell ablation of NTR-tagged cells in normal tissues.
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PMID:Aziridinyldinitrobenzamides: synthesis and structure-activity relationships for activation by E. coli nitroreductase. 1516 9